1. Field of the Invention
The invention relates to a switching arrangement for discharging an energy storage device of a motor vehicle, in particular for discharging an energy storage device that stores electrical energy and is provided so as to supply an electrical machine of a motor vehicle.
2. Description of the Related Art
Additional electrical energy storage devices are used in addition to or in lieu of a conventional 12V or 24V lead acid battery in mild hybrid, hybrid, and electric vehicles and these additional electrical energy storage devices are provided in the drive train to supply an electrical machine. An additional energy storage device of this type is frequently embodied as a lithium ion rechargeable battery or as a high capacity energy storage device. High capacity energy storage devices on the basis of double-layer capacitors are particularly favourable with respect to the capacity per mass. In this context, it is preferred that so-called ultra-capacitors are used, which are also referred to in short as ultracap or ultracap storage devices.
When using energy storage devices in the drive train with a high power capacity and low energy content, which for example ultra-capacitors are, these are normally charged up to nearly the maximum useful voltage prior to switching off the vehicle during the final braking procedure. Ultra-capacitors age most quickly in the high voltage state so that the serviceable life of the energy storage device can be adversely affected when storing energy storage devices of this type that have high charge voltages, in particular when the energy storage devices are fully charged.
On the other hand, it is not expedient from the energy point of view to automatically fully discharge the ultra-capacitor when switching off the motor vehicle or in a stop mode of a start-stop operation.